December 2022
Volume 22, Issue 14
Open Access
Vision Sciences Society Annual Meeting Abstract  |   December 2022
Neurophysiology and psychophysical studies of the stereo contrast paradox
Author Affiliations & Notes
  • Laura Palmieri
    NIH and Newcastle University
  • Jenny Read
    Newcastle University
  • Bruce Cumming
    NIH and Newcastle University
  • Footnotes
    Acknowledgements  Wellcome Trust, UK and NIH, NEI, USA
Journal of Vision December 2022, Vol.22, 3278. doi:
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      Laura Palmieri, Jenny Read, Bruce Cumming; Neurophysiology and psychophysical studies of the stereo contrast paradox. Journal of Vision 2022;22(14):3278.

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      © ARVO (1962-2015); The Authors (2016-present)

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Typically, stereoscopic disparity thresholds decrease for lower stimulus contrast. However, for low frequency luminance gratings, raising the contrast in just one eye impairs disparity thresholds more than if contrast is lowered in both eyes. This phenomenon, named stereo contrast paradox, is absent for high spatial frequency gratings and for stimuli that are frequency and orientation broadband. Using random dot (RDS) and random line stereograms (RLS), that are broadband in frequency and respectively broadband and narrowband in orientation, we investigated the activity of disparity-selective neurons in macaques primary visual cortex (V1) that perform the initial computations for stereopsis, and combined neuronal recordings with psychophysical measurements in primates and humans. Neurally, for RDS, disparity modulation is reduced more severely when contrast is lowered in both eyes compared to when it is lowered in just one, consistent with the absence of the paradoxical effect (median reduction factor 0.2 vs 0.4, pVal <0.001 sign rank test). However, for RLS, firing rates and disparity sensitivity were higher when contrast was low in both eyes than when it was mismatched between them, consistent with the presence of the paradox (0.7 vs 0.6, pVal < 0.001). To compare our physiology and psychophysics results, we introduced a neurometric discriminability d’ metric. Nevertheless, psychophysically, we found no paradox for either RDS or RLS in either humans or macaques, and replicated previous psychophysics results for RDS and gratings at different spatial frequencies. The discrepancy suggests that stereoacuity thresholds cannot be explained by a fixed linear decoder applied to V1.


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